The invention relates to a clutch actuation device using a hydraulic or pneumatic pressure to open or close a clutch with an oppositely directed operating movement.
DE 29 23 487 discloses an actuation device for a clutch, in which a piston, in conjunction with a cylinder filled with a pressure medium, opens a clutch. During a closing movement of the clutch, the piston is moved back into its initial position by a spring as part of the actuation device. The return movement is a consequence of the spring action travel.
An increase in the length of the return travel decreases, the force of the return spring. Consequently, the force of the return spring must be sized such that the initial position of the piston can be reached every time. A spring that is over designed, i.e. a spring that has an excess force, subjects the components of the actuation device to considerable stress. Thus, these components must be sized correspondingly robust.
DE 33 26 119 discloses that a plurality of piston/cylinder units can be used for the disengagement movement of a clutch.
DE 197 16 600 discloses an actuation device with an axially movable piston within a cylinder capable of being filled arbitrarily with a pressure medium which may be used for clutch actuation both by means of a tensile force and by means of a compressive force.
DE 197 00 935 A1 discloses an actuation device for a shiftable clutch. An electric actuator activates a master cylinder which, in turn, acts on a slave cylinder. It is further disclosed that if the actuator is combined with the master and the slave cylinder, opening and closing forces can also act actively on the clutch. Therein, the master and slave cylinder are arranged so as to be spatially separate. Thus, the medium displaced out of the master cylinder acts on the piston in the direction of extension of the slave cylinder.
When compressed air is used as the medium, no forces in the direction of retraction of the piston can be exerted by the slave cylinder when the piston of the master cylinder is extended. Since, compressed air is a compressible medium, retracting the slave cylinder piston does cause the master cylinder piston to extend. Only when a liquid is used as pressure medium can such a cause and effect occur.
It is an object of the present invention is to implement an actuation device for a clutch, which, even when the pressure medium used is compressed air, can exert opening and closing forces actively on the clutch.
This and other objects are achieved, when at least two piston surfaces are connected to the pressure supply device. The two piston surfaces execute an oppositely directed operating movement in the event of a pressure supply.
Since pressure is supplied to at least two piston surfaces, predetermined forces are transmitted, irrespective of the compressibility of the pressure medium. Thus, the actuation device can be operated with a defined excess pressure, in order, for example, to compensate for frictional effects on the moved parts.
It is an object to provide physically compact solution. Thus, the piston surfaces are arranged on a common piston. However, it is also possible of locating the piston surfaces on spatially separate pistons.
Furthermore, the two working spaces are arranged in a common cylinder. Thus, a double-acting cylinder may be used.
To activate the operating movement of the piston surfaces, the two working spaces are connected at least one flow valve. Alternatively, there is a possibility of each of the working spaces utilizing each a separately activatable flow valve.
During the opening or closing of the clutch, masses have to be moved. The inertia of the masses are disadvantageous for the useful life of the actuation device.
To produce specific feed and discharge conditions of the pressure medium, the operating movements of the piston surfaces can be braked in a specific way. For example, the outflow cross section or the times for the passage position of the valve for the decreasing working spaces may be reduced in a specific way, in order to utilize a counterpressure in that working space.
It is, therefore, advantageous that pressure sensing be performed in at least one of the two working spaces. Alternatively or in combination, with an earlier embodiment the travel of the piston surface during an operating movement may be detected by a travel sensing device. Consequently, the position of the piston surface and, therefore, also the instantaneous operating state of the shiftable clutch can be detected, irrespective of the compression behavior of the operating medium within the working space.
At least one of the working spaces may be arranged eccentrically to a transmission shaft. However, at least one of the working spaces may also be arranged concentrically to a transmission shaft.
Advantageously, the shiftable clutch may have a number of levers which are operatively connected to the pressure plate of the clutch. The levers are activated, in turn, by a transmission element which is operatively connected to the piston surfaces. The transmission element has transmission rings which act on the levers in an opening and a closing direction of the clutch. Consequently, the shifting movement of the clutch may be executed by means of a single transmission element.
There are at least two possibilities for the configuration of the levers. Thus, the levers may be prestressed in the closing direction of the clutch by a spring force. Thus, separate springs may be used which act on the levers, or levers with a specific spring action for example, diaphragm springs.
The levers my also be a means for force-free transmission. In this case, the closing force of the clutch must be generated completely by the piston surface in conjunction with the pressure medium in one working space. The levers can then be used as rigid pivoting levers.
Particularly with a view to simplifying assembly, the transmission rings are connected firmly to one another and form a continuous groove for receiving the levers of the shiftable clutch.
Furthermore, in an exemplary embodiment, the transmission rings are mounted so as to be axially displaceable in relation to the transmission element within a limited scope counter to a spring force. The axial displaceability likewise makes it substantially easier to assemble the clutch together with the actuation device.
Thus, the transmission rings are prestressed toward a holding surface by the spring force. For assembly in one direction, the holding surface is formed by a securing ring.
Alternatively, the transmission rings may be positioned against one stop and may be secured axially by means of a second stop.
To simplify manufacture, the second stop is formed by a peening over of the transmission element. A play-free connection is obtained between the transmission element and the transmission rings.
While a simple arrangement of rolling bodies may be sufficient for actuating a clutch the two piston surfaces may also be used to prestress an already closed clutch actively by means of utilization of the pressure supply device. For absorbing the forces associated with this, therefore, it may be expedient that a mounting which has a double-row arrangement of rolling bodies is formed functionally between the levers and the piston surfaces.
For a further increase in the permissible axial forces on the mounting, the center lines of the rolling bodies are formed in an X-arrangement with respect to their outer running surfaces.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.